Existing pen applicators generally utilize a twist function for dispensing a formulation from the pen applicator. These twist pen applicators generally include a rotating portion that is twisted or rotated relative to the remaining portion of the applicator, thereby advancing a formulation contained within the twist pen applicator. However, such twist pen applicators do not provide a predetermined dose of the formulation since the rotating portion is generally freely rotatable. Accordingly, a user is required to make a determination as to the appropriate amount of the formulation to dispense for a particular application. In addition, twist pen applicators may suffer from sealing problems. Further, such twist pen applicators generally require a substantial number of rotations of the rotating portion before the twist pen applicator is primed and ready to dispense the formulation.
Click pen applicators generally include an actuating portion that is pressed, or clicked, relative to the remaining portion of the applicator, thereby advancing a formulation contained within the click pen applicator. Further, such click pen applicators are conventionally known to have sealing problems that may render them less desirable than twist pen applicators, especially for formulations that may require better sealing, such as those that may tend to evaporate or experience weight loss over time. Further, click pen applicators also generally require a substantial number of clicks of the actuating portion before the click pen applicator is primed and ready to dispense the formulation. A prior art click pen 170 is illustrated in FIGS. 17 and 18.
Thus, existing pen applicators share the common problems of inadequate sealing, uncontrolled delivery of the formulation, and excessive number of actuations before the applicator is primed and ready for use. For example, inadequate sealing may result in the formulation's evaporating while the applicator is merely in storage between uses. In addition, uncontrolled delivery may result in a user's applying too much or too little of the formulation for the particular application, potentially having harmful or ineffective results. Further, excessive number of actuations for priming may lead to a user's believing that the applicator is broken, non-functional, empty, dried up, or otherwise unusable, when the applicator is in fact functional but not yet fully primed for use.